1. Field of the Invention
The invention relates an illumination device, and more particularly to, a light emitting diode device.
2. Description of Related Art
Light emitting diode is usually composed of semiconductor materials containing groups III-V elements, and the light emitting diode has the ability of converting electrical energy into light. The luminescence of the light emitting diode belongs to cold luminescence; therefore, the light emitting diode has the advantages of fast response, small size, power-saving, and difficult to break, and thus the application field thereof is very broad.
The gallium nitride based (GaN-based) semiconductor material has been proven to have a great potential in the application of producing the light emitting diode, and the coverage of the light emitting wavelength thereof may range from infrared light, visible light, and to ultraviolet light. Therefore, GaN-based semiconductor is increasingly valued by the majority in the recent years.
The conventional gallium nitride light emitting diode usually uses sapphire as epitaxial substrate. However, the sapphire is transparent material, causing light emitted by the light emitting diode to scatter around, incapable of concentrated utilization, and thereby reducing the light emitting efficiency of the light emitting diode. Furthermore, since refractive index of outside air and the gallium nitride material differs about 1.5, light generated by the light-emitting layer of the light emitting diode is totally reflected by the interface of the gallium nitride and the outside air, thus being limited in the internal of the light emitting diode, so that the light emitting efficiency of the light emitting diode is reduced.